Photo-tagging (also known as photo-classification or photo-indexing) is a process of matching photographs to the photographed people in them. This process frequently takes place in mass participation events such as competitions (running, cycling, triathlons etc.), branded events (such as experiential marketing activations, concerts, corporate events, trade shows etc.) and visitors attractions (as amusements parks, museums etc.).
The event organizers arrange to take photographs of the event participants and then offer participants access to the photos they appear in. The event photos can be offered to participants either for free or for a fee.
At present, at many mass-participation events, photo-tagging is performed manually. That is, a person goes over each photo and identifies the participants in the photo via their participant identification, for example, a number on a participant bib-number (chest-number) or plates with unique participant numbers. The manual process, performed by humans, can be slow and error-prone.
In certain sporting events such as road bicycle tournaments, there is little room to place a participant identification number in a visible position. This limits the option of human based photo-tagging in such events.
Another alternative used today is to tag a photo with a timestamp of the event. For example, in a race, the timestamp since the race launch. This method is limited to racing-type events and is error-prone due to gaps between the timing of the cameras and the official timing of the race. Also, in large races, people are launched at different times (first the professionals/fastest runners etc.) thus there is no unique timestamp from a launch. This method is also limited to taking pictures at certain locations of the race, best of them is typically the finishing line, where every participant remembers the time he made. This method does not lead itself for automatic participant recognition, but rather for people manually looking for their own picture. For example, if you know you finished the race in 55:10 minutes, you can look for pictures showing the end line with the time close to the time you made.
Another alternative for the timestamp matching described above is to match the photograph shooting time with timing system records, typically based on Radio Frequency Identification (RFID) chips carried by participants and read by RFID-mats that read the RFID chip when a participant steps over the RFID-mat. This method can be automated by sending a photograph taken at time X to the participant who's RFID timing was recorded at X. However, this method is error prone because of gaps between the RFID timing and camera timing. Even a gap of 1-2 seconds in a race, can lead to a picture showing another participant. Automatically posting photographs, for example on a social network, showing the wrong participants is something to be avoided.
In non-sporting events (such as festivals) the options for photo-tagging are very limited at present. A common practice is to collect personal contact information (e.g.—email) of the photographed people just after taking their photos. This process slows down the event photography operation. Another common practice is to place all the event photographs together, and let each participant browse through all the photographs and identify himself photographs he appears on. This is obviously a cumbersome and error-prone process.